Insights into multistep depressurization of CH4/CO2 mixed hydrates in unconsolidated sediments

Path-dependent morphology of CH4 hydrates and their dissociation studied with high-pressure microfluidics

“…4b shows the P-T trajectory in relation to the MH phase equilibrium curve. As can be seen, the sub-cooling (T sub ) of MH formation at the pore-scale in this process was ∼10.2 K. It was interesting to note that the T sub required to induce MH formation on the microfluidic chip (in the range of 10-15 K) 20 was usually higher than that in actual marine sediments (in the range of 3-8 K). 36 This can be possibly attributed to two reasons: (a) the existence of impurities in marine sediments (such as montmorillonite minerals) promotes heterogeneous nucleation and reduces both the induction time and T sub .…”

“…19 The direct visualization of the MH interface and gas bubble evolution during MH dissociation is essential for addressing the rate of MH dissociation. 20,21 Kou et al 17 conducted X-ray experiments that revealed that the water layer covering the MH grows during MH dissociation. These findings show that the thickness of the water film at the front of the MH dissociation interface and the evolution of gas bubbles increase the complexity of the mass transfer.…”

Review and Perspectives of Energy-Efficient Methane Production from Natural Gas Hydrate Reservoirs Using Carbon Dioxide Exchange Technology

“…At the same time, it can be used as a single method or combined with other production techniques without significant interference between them. Depressurized production is employed in different variations such as constant rate depressurization, , cyclic decompression and slow multistage depressurization. , It is always the preferred method in every production test due to its efficiency and improved dissociation performance. However, there are some inherent disadvantages to rapid depressurization, especially during the early phase of production (limited permeability), such as excessive sand production and borehole freezing along with expedited re-formation of the hydrate, preventing it from being used alone.…”

“…Salinity, fluid movements, permeability, and intrinsic sediment properties may influence the stability of CO 2 hydrates. A six-stage multistep depressurization technique was experimented with by Ouyang and team using different gas compositions on unconsolidated sediment. They found that CO 2 gas preferred to take its hydrate form much faster than CH 4 .…”